% -*- texinfo -*-
% @deftypefn {Function File} {} conditionalentropy_YX (@var{xy})
%
% Computes the
% @iftex
% @tex
% $H(\frac{Y}{X}) = \sum_i{P(X_i) H(\frac{Y}{X_i})$, where
% $H(\frac{Y}{X_i}) = \sum_k{-P(\frac{Y_k}{X_i}) \log(P(\frac{Y_k}{X_i}))$.
% @end tex
% @end iftex
% @ifnottex
% H(Y/X) = SUM( P(Xi)*H(Y/Xi) ), where H(Y/Xi) = SUM( -P(Yk/Xi)log(P(Yk/Xi)))
% @end ifnottex
% The matrix @var{xy} must have @var{y} along rows and @var{x} along columns.
% @iftex
% @tex
% $X_i = \sum{COL_i}
% $Y_i = \sum{ROW_i}
% $H(Y|X) = H(X,Y) - H(X)$
% @end tex
% @end iftex
% @ifnottex
% Xi = SUM( COLi )
% Yi = SUM( ROWi )
% H(Y|X) = H(X,Y) - H(X)
% @end ifnottex
% @end deftypefn
% @seealso{entropy, conditionalentropy_XY}